A well-recognized problem in hospital care is that wounds caused by surgery or accidents, in spite of having been properly closed and dressed, may start to bleed again. Due to the dressing by which the wound is covered or due to the patient being unconscious or otherwise unable to recognize the bleeding, it is only noticed by the staff and taken care of after a while. In the meantime the patient may have lost a substantial volume of blood. This will no doubt have a detrimental effect on his or her recovery.
Another problem of similar kind is quite frequently seen in blood dialysis. In a life saving treatment patients with impaired or non-existing renal function purify their blood from salts, urea and other metabolic degradation products on a regular basis, such as two or three times per week. In blood dialysis an artery is punctured by a cannula or needle to make a portion of the patient's blood pass through a dialysis apparatus in which it is purified. The purified blood is returned to the patient by venous infusion through a cannula inserted into a large vein. Most often arterio-venous fistula (or a corresponding graft) is created at a patient's wrist or upper arm, from which blood is removed by an arterial cannula and returned downstream by a venous cannula.
A cannula of this kind usually comes with wings extending from a short cylindrical plastic tube in which the cannula is mounted. These wings can be used for securing the cannula by adhesive tape to prevent it from longitudinal displacement in the vein, fistula, or graft. The adhesive tape may accidentally come off and the cannula withdrawn. Inevitably this results in immediate bleeding, which may be quite severe. If the bleeding is not noticed and stopped at once the patient may lose a large volume of blood. Since dialysis patients are usually anaemic, they are particularly affected by such a loss. In addition it is important to prevent blood contained in the dialysis apparatus from being lost if a cannula is removed accidentally. To cope with a loosening arterial needle a safety means is included in known dialysis apparatus. The safety means comprises a pressure sensor disposed on the input side of the apparatus. If the sensor detects a sudden drop in pressure during dialysis the flow of blood through the apparatus is immediately stopped and the personnel alarmed. Due to the pressure drop in the venous needle a loosening thereof cannot be monitored easily in a corresponding manner.
WO 06/001759 A1 discloses a method for detecting blood leakage from a wound in which a sharp bend of an optical fiber is disposed at the wound. Light passing through the fiber is detected at one end of the fiber. Leaking blood contacting the fiber attenuates the passing light. The attenuation, which indicates blood leakage, is detected and an alarm is triggered. The method of WO 06/001759 A1 employs a device comprising an optical fiber and a medical patch. For hygienic reasons the device is disposable.
The provision of alternative methods of detecting blood leakage from a wound not employing a disposable device or a disposable device, which is more economical and/or simpler to manufacture than the prior art device is desirable.